Half inch of sag and hairline cracks - did I remove a load-bearing wall?

sounds to me like it was load bearing, but if it is a opening larger than a double doors i would of imagined the sag would of happened sooner than 2 year later. a couple checks you can do to give yourself some peace of mind. go upstairs above the opening in question and knock on the wall above it, if there is one that is. if the wall sounds hollow then i wouldn't worry, if is likely a partition wall of timber. if the wall sounds solid and has a dull thumb sound to it, it is likely made from bricks, stone or blocks, and will be load bearing. a good way to check for sure is to drill a hole into the wall so see if its solid masonry or not. 2nd is to lift the carpet in the room above to see what direction the floorboards are laid. if the ends of the floorboards are laid towards the wall which you removed below, then that means the joist ends are supported by the opposite walls, and so not load bearing down onto the demolished wall. if the floor boards are running in the opposite direction, be it parallel to the demolished wall, then that means the joists are set into the wall you demolished. if so it need propping with some acro poles available for less than £5.00 per week from a hire shop. best advice though is to get a local builder in to take a look for you.